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xen: support sysenter/sysexit if hypervisor does

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64-bit Xen supports sysenter for 32-bit guests, so support its
use.  (sysenter is faster than int $0x80 in 32-on-64.)

sysexit is still not supported, so we fake it up using iret.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jeremy Fitzhardinge
2008-03-17 16:37:17 -07:00
committed by Ingo Molnar
parent aa380c82b8
commit e2a81baf66
6 changed files with 99 additions and 3 deletions
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56
arch/x86/xen/xen-asm.S
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@@ -280,6 +280,62 @@ ENTRY(xen_iret_crit_fixup)
2: ret
ENTRY(xen_sysexit)
/* Store vcpu_info pointer for easy access. Do it this
way to avoid having to reload %fs */
#ifdef CONFIG_SMP
GET_THREAD_INFO(%eax)
movl TI_cpu(%eax),%eax
movl __per_cpu_offset(,%eax,4),%eax
mov per_cpu__xen_vcpu(%eax),%eax
#else
movl per_cpu__xen_vcpu, %eax
#endif
/* We can't actually use sysexit in a pv guest,
so fake it up with iret */
pushl $__USER_DS /* user stack segment */
pushl %ecx /* user esp */
pushl PT_EFLAGS+2*4(%esp) /* user eflags */
pushl $__USER_CS /* user code segment */
pushl %edx /* user eip */
xen_sysexit_start_crit:
/* Unmask events... */
movb $0, XEN_vcpu_info_mask(%eax)
/* ...and test for pending.
There's a preempt window here, but it doesn't
matter because we're within the critical section. */
testb $0xff, XEN_vcpu_info_pending(%eax)
/* If there's something pending, mask events again so we
can directly inject it back into the kernel. */
jnz 1f
movl PT_EAX+5*4(%esp),%eax
2: iret
1: movb $1, XEN_vcpu_info_mask(%eax)
xen_sysexit_end_crit:
addl $5*4, %esp /* remove iret frame */
/* no need to re-save regs, but need to restore kernel %fs */
mov $__KERNEL_PERCPU, %eax
mov %eax, %fs
jmp xen_do_upcall
.section __ex_table,"a"
.align 4
.long 2b,iret_exc
.previous
.globl xen_sysexit_start_crit, xen_sysexit_end_crit
/*
sysexit fixup is easy, since the old frame is still sitting there
on the stack. We just need to remove the new recursive
interrupt and return.
*/
ENTRY(xen_sysexit_crit_fixup)
addl $PT_OLDESP+5*4, %esp /* remove frame+iret */
jmp xen_do_upcall
/*
Force an event check by making a hypercall,
but preserve regs before making the call.